What's the right spec for relaying my slab for wet UFH

[Mechanical Mike]

In our Victorian semi the back of the house has a solid floor. It's about 50m sq over 3 rooms. I want to fit under floor heating and i'm dubious about the overlay systems on offer because of the thinness of the insulation. I've been advised that to do it properly I should dig out the floor slab and relay it on a dpc. Then lay insulation , then fit the UFH pipes which are then re covered in a sand cement mix. after that I can get the floor levelled ready for large floor tiles. My question is what are the correct specifications and thicknesses for the various components. Ie. how thick should the slab be, should the dpc be under the concrete or just the insulation? What is the spec for the insulation? Is it king span type rigid foam ? If someone could point me at some literature it would be much appreciated.

 

[Agile]

There is a lot of variation but generally would be a little blinding sand, DPC, about 60 mm concrete, ideally 100 mm insulation then the UFH pipes covered by a total depth of 50-60 mm.

The makers of the UFH pipes will usually have their advice on their web site.

But that needs to be considered in relation to the soil conditions in your property.


Tony

 

[Mechanical Mike]

Thanks for the reply. Is there a typical spec for the insulation?
Is there any special detailing at the edges of the room where the insulation &dpc meet the wall?

 

[Faceache]

Celotex FF 4000 for the insulation which is manufactured specifically for UFH applications.
10mm edge insulation against wall edges. You can buy this with a self adhesive back to aid installation.
Lay the insulation.
Layer of polythene sheet on top of insulation boards taped at joins to prevent screed slipping between boards.
Lap the polythene sheet up in front of the edge insulation.
Screed min 65 mm 4:1 mix.
This is what I do. No doubt others do it differently.

 

[Mechanical Mike]

Thanks for the advice so far. Time to get on with it. One last question . I need an internal stud wall as well in the same area. Do I install this on top of the UFH screed. ( Having laid the pipes to avoid the fixings) Sorry if it's a daft question.

 

[Agile]

Celotex FF 4000 for the insulation which is manufactured specifically for UFH applications.
10mm edge insulation against wall edges. You can buy this with a self adhesive back to aid installation.
Lay the insulation.
Layer of polythene sheet on top of insulation boards taped at joins to prevent screed slipping between boards.
Lap the polythene sheet up in front of the edge insulation.
Screed min 65 mm 4:1 mix.
This is what I do. No doubt others do it differently.

Does that mean that you would not have a dpc UNDER the Celotex?

Or are you assuming there is already a concrete subfloor over a dpc?

Tony